The first thing that strikes you about the Canon 28-70mm f2.8L is it’s size. This is a big heavy chunk of glass, with the biggest lens hood I’ve ever seen on a lens of this spec. It feels very well made although the zoom action is only smoothish, not absolutely even. It stiffens slightly at the wide end. Part of the reason for this and the huge hood is that the front of the lens extends quite some distance as you reach 28mm. This lens was replaced by the 24-70 f2.8L some time ago, but as it appears built to last a lifetime, I’d have no worries about buying a used one.
Canon’s L series of lenses are famous for their optical quality, but most, like this one, were designed for film - So how does it perform with the Canon EOS 20D?. The short answer is - extremely well - not perfect, but pretty close. Full aperture results at 28mm at first glance look softer than I expected, but with a little careful sharpening, even these look great. Full aperture resolution is better from 35mm on although corners are very slightly soft throughout the range particularly in areas of high contrast. The area affected by this is smaller than with most lenses though.
Even at full aperture central sharpness levels are maintained until about 70% of the distance to the corner. It really goes without saying that well stopped down to f5.6 and beyond performance is superb.
Full Frame DSLR Test